Noncrystalline polyarylates comprising units derived from 2,2-bis(4-hydroxyphenyl)propane (also referred to as bisphenol A) and units derived from terephthalic acid and isophthalic acid are well known as engineering plastics. Such polyarylates have high heat resistance, excellent mechanical strength as represented by impact strength and dimensional stability, and are also noncrystalline and transparent Molded articles thereof are therefore finding wide application in various fields of the electric, electronic, automobile and machine industries.
Furthermore, polyarylate resins made from bisphenol A as a raw material for a divalent phenol (referred to as bisphenol A polyarylates) have been applied to the production of electronic parts such as films for capacitors by utilizing their good solubility in various solvents and excellent electrical characteristics (insulating properties and dielectric characteristics) and wear resistance. Such polyarylate resins have also been used for forming various coating films and as coating resins for liquid crystal displays by utilizing their wear resistance and scratch resistance.
In the fields of films and the like requiring surface gloss or in the application of coating materials and the like forming coatings, there has been an increasing demand for resins having improved electrical characteristics and wear resistance. However, the bisphenol A polyarylates when used in some applications are deficient in these characteristics.
British Patent 901,605 describes a polyarylate which possibly solves such problems composed of 2,2-bis(3-methyl-4-hydroxyphenyl)propane (also referred to as phenol C) and terephthalic acid, and having an intrinsic viscosity in tetrachloroethane of 0.84. However, this patent publication does not refer to the wear resistance of the polymer. Furthermore, the polyarylates described in the examples of British Patent 901,605 are brittle because their only acid component is terephthalic acid, and they have insufficient wear resistance because their intrinsic viscosity is about 0.84.
Furthermore, JP-A-9-22126 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") describes an electrophotographic photoreceptor using a polyarylate composed of bisphenol C, terephthalic acid and isophthalic acid, and having an inherent viscosity in tetrachloroethane at a concentration of 1 g/dl at 25.degree. C. of 0.833, as an example. The electrophotographic photoreceptor using this polymer still has a low molecular weight, so that it has insufficient wear resistance as a resin for coating formation. JP-A-9-22126 further describes an electrophotographic photoreceptor using a polyarylate having an inherent viscosity of 1.241 which provides excellent wear resistance. However, it is pointed out that a coating solution of this polyarylate has poor storage stability. Furthermore, this polymer having an inherent viscosity of 1.241 is a polymer synthesized using tetramethylbenzylammonium chloride as a catalyst, and therefore has a high carboxyl value which gives rise to a problem in electrical characteristics. Furthermore, the poor storage stability of the coating solution is also caused by its high carboxyl value.
In view of the above, there is a need for resins for coating formation having excellent wear resistance and electric characteristics, as well as a coating solution thereof having good storage stability.